The digital communications receiver function of equalization is part of many modern telecommunications platforms. For instance, equalization is instrumental in proper return operation in Data Over Cable System Interface Specification (DOCSIS) systems. The term DOCSIS refers to a group of specifications that define industry standards for cable headend and cable modem equipment. In a DOCSIS network, upstream channel impairments can be mitigated by equalization.
During equalization, an equalizer generates coefficient information that is used to create an equalizing filter, with an inverse channel response, canceling distortion in the channel caused by upstream channel impairments. The equalization coefficients of DOCSIS can be 24 symbol-spaced coefficients (also referred to as taps).
Analysis of the equalization coefficients used to create the equalizing filter may be used to diagnose network issues. For instance, many cable operators participate in CableLabs' Proactive Network Maintenance (PNM) committee and are evaluating integration of this type of technology into their existing diagnostic systems because it is believed that equalization coefficient analysis may improve diagnostic efficiency.
A “proactive” aspect of equalization coefficient analysis comes from the ability to identify network problems before traditional metrics, including Modulation Error Ratio (MER), Transmit Power, Receive Power, Forward Error Correction (FEC), and Codeword Error Rate (CER).
However, statistical methods of interpretation used for equalization coefficient analysis are not without problems. For instance, when multiple upstream impairments are present, impairment characteristics are almost always misdiagnosed because the current process used for equalization coefficient analysis is limited to statistical analysis of frequency domain characteristics of an impaired equalization response. Thus, problems with the analysis are greatly exacerbated when multiple impairments are being experienced thereby reducing diagnostic capability.